Display devices with touch sensitivity are used today in a wide variety of applications such as touch pads in laptop computers, all-in-one computers, mobile phones and other hand-held devices, etc. It is often a desire to provide these electronic devices with a relatively large touch sensing display and still let the devices be small and thin.
There are numerous techniques for providing a display device with touch sensitivity, e.g. by adding layers of resistive wire grids or layers for capacitive touch-sensing or by integrating detectors in the display device. The major drawback of these techniques is that they reduce the optical quality of the display device, by reducing the amount of light emitted from the display or by reducing the number of active pixels of the display device.
U.S. Pat. No. 7,432,893 discloses a touch sensing system that uses FTIR (frustrated total internal reflection) to detect touching objects. Light emitted by a light source is coupled into a transparent panel by a prism, then propagates inside the panel by total internal reflection where after the transmitted light is received at an array of light detection points. The light may be disturbed (frustrated) by an object touching the panel, whereby a decrease in transmitted light is sensed at certain light detection points. Providing a display device with this touch sensing system would add an undesired thickness and complexity to the display device.
WO2009/077962 also discloses a touch sensing system that uses FTIR to detect touching objects. Disclosed is a panel with a tomograph having signal flow ports adjacent the panel, the flow ports being arrayed around the border of the panel. Light is emitted into the panel by the flow ports and propagates inside the panel by total internal reflection where after the transmitted light is detected at a plurality of flow ports. The light may be disturbed by an object touching the panel. Providing a display device with this touch sensing system would add an undesired thickness and complexity to the display device.